2 answers

Secure Gateway - Tunneling service to your back end system. Bluemix cloud host will act as gateway to your backend system.

Cloud Integration - Create Rest APIs from your back end system.

Cloud Integration does include similar capability of "Secure Gateway" in basic connector. But I heard it might be replaced to Secure Gateway, since secure gateway provides better handling of multiple connections to back end system. As a result, "Cloud Integration" is used when you want to expose the data or system via RestAPIs.

Secure Gateway is a technology that for the most part replaces the Cloud Integration Basic Connector. It provides basic and TLS protected tunnels to your on-premises resources. It is the strategic cloud communication solution for Bluemix moving forward. More information can be found here: https://www.ng.bluemix.net/docs/services/SecureGateway/index.html